Niels J. van der Veen, Richard J. M. Egberink, Johan F. J. Engbersen, Frank J. C. M. van Veggel and David N. Reinhoudt
Soft metal ions like Pb2+, Cd2+, and Cu2+ form partial-cone complexes with a flexible calix[4]arene chromoionophore in which cation–π interactions cause a bathochromic shift of the UV/Vis absorption maximum.